The present invention relates to a process for the preparation of olefinically unsaturated ethers from conjugated dienes and alkanols. The present invention relates in particular to a process for the preparation of butenylethers from butadiene and lower alkanols. The unsaturated ethers produced may be used as such, e.g. as solvents or as gasoline additives or may serve suitably as starting materials for chemical processes such as the conversion into the corresponding saturated ethers or into ketones.
It is known from U.S. Pat. No. 2,922,822 that alkenyl ethers can be produced by reacting conjugated dienes and lower alkanols in the presence of an acidic ion-exchange resin. Suitable reaction conditions comprise a large excess of alkanol which does not only serve as the reactant but also as the solvent. In the process for the preparation of butenyl-ethers from butadiene and lower alkanols as disclosed in German Offenlegungschrift No. 2,330,902 preference is given to a butadine/alkanol ratio of 1:2.
The above-mentioned processes however, suffer from the serious drawbacks that large amounts of unwanted by-products are formed under the reaction conditions. From Example 1 of German Offenlegungschrift No. 2,550,902 it appears that the butadiene-dimer 4-vinylcyclohexene (VCH) is even formed as the main product, thus wasting valuable starting material. In repeating the process described in U.S. Pat. No. 2,922,822 it was found that a substantial amount of low boiling dimethylether (DME), even as high as 51% based on methanol consumed, was found which renders the process on a large scale inadequate for the preparation of olefinically unsaturated ethers.